Fluid bed process for coking hydrocarbons



United States Patent Delaware No Drawing. Filed Dec. 13, 1963, Ser. No. 330,236

Claims. (Cl. 208-127) This invention relates to a high temperature process of cracking hydrocarbons to produce coke. The invention relates to a fluid coking process for cracking hydrocarbons to produce coke and hydrogen wherein the production of soot-like material is substantially reduced. This invention specifically relates to a high temperature coking process for cracking hydrocarbon feeds wherein the hydrocarbon feed is injected into a fluid bed of hot coke particles and cracked to produce hydrogen and to deposit coke on the fluidized coke particles and wherein soot-like material production is reduced and the reaction is made selective to high quality coke product. More particularly, in accordance with the present invention, the hydrocarbon feed is injected into a fluidized bed of coke, said coke being at a temperature of between 1800 to 3000 F. at a sufficient rate to maintain the average superficial linear gas velocity of the gaseous products at between about 0.1 to 0.7 ft./sec. The feed is cracked to produce hydrogen which comprises the fluidizing gas and to deposit coke on the hot coke particles.

During the high temperature fluid coking process of cracking hydrocarbons to produce high quality coke, a poor quality thermal black soot-like material is produced in addition to coke. The soot-like material can comprise up to to 75% by weight of the carbon produced. This material is too large for use as thermal black and is too poor in quality to be used in the manufacture of coke electrodes for the aluminum industry. In addition, the soot-like material is frequently entrained in the fluidizing gas and results in overhead plugging limiting operation of the coking equipment to short periods of time. The production of soot-like material decreases product coke yield. Also, it is difficult to recover the soot-like material in normal gas solids separating devices such as cyclones and much of the soot is released to the atmosphere causing polution. The problem of soot manufacture is unique to high temperature cracking reaction carried out at temperatures of 1800 to 3000 F. Heretofore, it has been a practice to fluidize fluid coke beds at gas velocities of about 1 to 3 ft./ sec. in a low temperature fluid coking process carried out at 900 to 1400" F. Under these conditions there was no soot production. However, if fluidization was carried out at these rates in the high temperature process, the soot make would be substantial at temperatures above 1800 F. and the process would be uneconomical due to low coke production.

Applicants unexpectedly found that the production of soot-like material is the result of gas phase cracking at temperatures above 1800 P. which occurs in the dilute (or disperse) phase above the fluid bed and in the void volume of the dense phase fluid bed, that is, in the gas bubbles in the fluid bed. These bubbles are formed from the fluidizing gas and are directly related, that is, the bubble size to the average fluidizing gas velocity through the bed. Applicants also found that the reaction from which soot is produced, which occurs in the fluid bed, is dependent upon the average superficial linear gas velocity through the bed and the reaction temperature. The amount of soot produced at a specified average gas velocity will vary somewhat with the temperature and the amount of soot produced at a specified temperature will vary somewhat with the average gas velocity.

In accordance with the present invention, high qualityhigh temperature hard coke product of relatively large particle size is obtained and hydrogen recovered as a byproduct under conditions whereby the amount of soot produced from the cracking reaction is substantially reduced. The high temperature fluid coking process of the present invention can be carried out in a suitable coking reactor used in conjunction with a transfer line burner which provides the heat to the coking step by burning fuel in the burner which heats the coke, which coke is circulated back to the reactor. Electrode resistance heating can be used to provide heat directly to the reactor. Another suitable process is one in which the coke is cracked in a large diameter vessel and the hydrogen product is burned in the top of the vessel and the coke is heated by radiant heat from the combustion flame of hydrogen and air and reflected heat from the roof and walls of the reactor.

The coke particles in the fluid bed are maintained at a size suitable for fluid'ization by grinding part of the product coke to seed coke. The hydrocarbon feed fed into the bottom of the coke bed on contact with the hot coke particles immediately vaporizes the feed and it is cracked to deposit carbon on the coke particles and to liberate hydrogen gas. This hydrogen gas can be recovered and/ or can be used as a fuel. The evolved hydrogen gas comprises most of the fluidizing gas in the-coke bed. Hydrocarbon is fed at such a rate that the average superficial linear velocity of the fluidizing gas is maintained within the critical limits described in the present invention. The average gas velocity, however, is the average velocity of all the gases in the bed, which can include vaporized hydrocarbons, cracked hydrocarbons, moisture, methane, etc.

In order to obtain practical feed throughput, it is preferred to use relatively large diameter fluid beds with multiple feed inlet means. The use of low fluidizing gas velocities minimizes fines entrainment in the dilute phase, minimizes bubble size in the dense fluid bed phase, and substantially reduces the production of soot at the high temperatures used in accordance with the present invention. Seed coke is continuously added to the fluid bed to maintain the average coke size in the bed. During the reaction coke is deposited on the coke particles and as the coke particles increase in size and as the bed builds up, product coke is withdrawn. A high-quality, highdensity hard coke product of relatively large size is recovered from the process with a minimum amount of soot production. The process is not limited by the particular type of coking apparatus utilized to carry out the process and any suitable apparatus can be used.

The present invention-solves several problems encountered in high temperature fluid coking. By carrying out the coking at these high temperatures and at relatively low average superficial linear gas velocities in the coke bed, the production of soot-like materialis greatly reduced, thus making the process more economical. The reduction of soot make greatly increases the coke yield from the process. The reduction of soot make also greatly minimizes air pollution due to soot carryover in the entrained fluidized gases. The invention provides a method for obtaining high quality fluid coke at high ields. y The hydrocarbon feed to the high temperature fluid coking process to make coke and hydrogen can be any gaseous liquid or heavy residual hydrocarbon. Vacuum residuum as well as residua, which are solid at ambient temperatures, can also be used. Also, the process can utilize mixtures of gaseous or liquid hydrocarbon feeds. Heavy hydrocarbon oil feeds that are suitable for coking processes are heavy or residual crudes, vacuum bottoms, pitch, asphalt, and other hydrocarbon petroleum residuum 3 mixtures thereof. Depending on the location and source of feed available, naphtha and gas oil can also be used. Typically, such feeds have initial boiling points of around 700 or higher, an API gravity of to 20, and a Conradson carbon residue content of about 5 to 40 wt. percent.

Hydrogen is produced as a by-product of the cracking reaction and can be available in purities of 87 to 98%, depending upon the temperature and pressure at which the cracking reaction is carried out. Small amounts of methane may be present in the fluidizing gas. Also, there may be present some impurities from hydrocarbons, such as sulfur and hydrogen sulfide. The hydrogen can be recovered and purified and used in refining processes utilizing hydrogen, or used for chemical uses. The hydrogen can also be used as a fuel in a transfer line heater or in a radiant heater reactor, in which case the purity of the hydrogen Would not be a problem. The solid coke particles produced in accordance with this process are relatively large homogeneous hard particles. The coke product has unique physical properties which permit it to be used directly in the formation of carbon electrodes without subsequent thermal treatment such as calcining. The physical properties of the coke permit its use in the formation of improved coke bodies of high density. The high temperature coke produced in accordance with this invention has high density, low porosity and relatively large particle size. The coke also is generally spherical in shape and made up of a laminar structure which can comprise 30 to 100 superimposed layers of coke which is deposited at the high temperatures used in the coking reaction. A photo-graph of a cross-section of the coke reveals a tightly packed onion skin appearance. A close examination of photo-micrographs shows absence of voids from the coke particles.

The coke produced in accordance with this invention has a density, by hydrocarbon displacement, of 1.80 to 1.93 grams per cc. The density of 48 to 100 mesh coke particles packed in a 150 cc. tube is 1.25 to 1.35 grams per cc. They have a calculated void volume of 25 to 35%, and an electrical resistivity of 0.020 to 0.050 ohminch.

The particle size distribution of the high temperature coke particles varies with the conditions at which the coking step is carried out. The coking process is carried out in such a manner that about 90 wt. percent of the solids fall within the particle size range of about 20 mesh to 200 mesh with less than about wt. percent of the particles falling outside of this size range.

The particle size distribution which can easily be fluidized at average linear superficial gas velocities of 0.1 to 0.7 ft./sec. are shown below mogether with the particle size to which the seed coke must be ground to maintain the desired average size in the bed.

Table I Wt. percent on: 10 Mesh Mesh Mesh Mesh- Mesh- Mesh. Mesh- Mesh. 5-15 5-10 Mesh 5-10 10-30 200 Mesh 5-10 10-30 300 Mesh 1-5 20-30 Through 300 Mesh 1-5 5-10 The soot-like material that is produced at the high temperatures of 1800 to 3000 F. at superficial linear gas velocities, substantially above those preferred by aplicants, or even the 5 to 10% soot produced at the superflcial linear gas velocities preferred by applicants, can be described as follows: The soot-like material resembles carbon black but is substantially larger than the carbon black and has a particle size range of about 800 to 8000 A. and an average particle size of about 2500-3500 A. This material is too large to be used as carbon black and of such poor quality that it cannot be used as coke for making coke electrodes or other coke formulations. The soot m-aterial is soft, highly porous, and has a very loW density.

The average particle size of the coke particles in the fluid bed can be bet-ween about -600 microns, and preferably about 200-350 microns. This results in Withdrawal of coke particles having a relatively large average size. In order to maintain the average size desired in the coke bed to assure good fluidization of the bed at the relatively low superficial linear gas velocity used in accordance with the present invention, a fifth to one-third of the net coke make of the reaction is ground to make seed coke which is fed back into the fluid coke in the bed. The seed coke will be ground to an average size of about 50-120 microns, and preferably about 75-100 microns. To obtain sufficient throughput of hydrocarbon feed at the relatively low superficial linear gas velocities used, it is generally preferred to use a relatively shallow .bed of wide diameter. The bed depth can be 5-20 feet, more generally 6-15 feet, and preferably about 10 feet with a bed diameter for adequate feed throughput being 5-70 feet, more genera-11y 10-60 feet, and preferably 40- 50 feet. The bed depth is selected to give 95-98% conversion of hydrocarbon feed to carbon and hydrogen.

The soot production problem is unique to the high temperature coking reaction and is not prevalent at the conventional low temperature fluid coking reaction temperatures of 900 to 1400 F. The soot-make Was not a problem until the coking reactions were carried at temperatures above about 1800 F. In order to obtain the improved coke product having the unique physical characteristics of applicants high temperature coke, it is necessary to carry out the co 'ng reaction at temperatures of 1800-2500, generally 1950-2300, and preferably 2100- 2200 F. Coking reactions carried out at lower temperatures result in a coke product, which is substantially different from the coke product obtained in accordance with the present invention. The average superficial linear gas velocity of the fluidizing gas, consisting essentially of hydrogen and minor amounts of methane, is critical and is carefully controlled within the range of 0.1-0.7 ft./sec., generally 0.2-0.5, and preferably 0.3-0.4. By carefully controlling the gas velocity, the soot-make or soot promatter of convenience. Depending on the particular hydrocarbon feed used and the purity of hydrogen desired, it may be preferred to carry out the coking reaction at superatmospheric pressures. However, the coking reaction can suitably be carried out at pressures of 0-20 atm., more generally 0-10 atm., and preferably 1-2 atm.

lated to the average superficial linear gas velocity of the fluidlzing gas and the temperature at which the coking reaction is carried out. The temperature and superficial linear gas velocities are heater burner vessel. In a typical operation the hydrocarbon to the process is injected into the reactor vessel containing a dense, turbulent, fluidized bed of hot coke particles. Uniform mixing in the bed results in virtually isothermal conditions and effects instantaneous distribution of the feed stock. In the coker, the feed stock is cracked essentially to hydrogen and coke. The heat for carrying out the endothermic cracking reaction is generated in the burner vessel. A stream of coke from the reactor is transferred to the burner vessel, for example, a transfer line burner employing a standpipe riser system, a suitable gas being supplied to the riser for conveying the coke solids into the burner. An extraneous carbonaceous fuel or by-product hydrogen used as fuel is burned in the burner vessel to bring solids therein up to a temperature suflicient to maintain the system in heat balance. The solid-s in the burner are maintained at temperatures of about 200 to 400 F. above the reactor temperature, depending upon solids circulation rate. The net coke make above that needed to maintain the inventory necessary for circulation to provide heat is withdrawn. A portion is ground to use as seed coke to maintain the desired average coke particle size in the reactor and is returned to the reactor.

Another type of reactor vessel that can be used is one in which the fluid coke bed is heated by radiant heat from the combustion of the by-product hydrogen and air in the upper part of the same vessel. Construction of such a reactor vessel is important in that the geometry of the vessel is such that the diameter of the fluid bed is relatively large and the depth of the bed is relatively shallow and is such that radiant heat from the combustion flame will be radiated into the fluid bed of coke particles as Well as reflected radiant heat from the walls and roof of the reactor. This type of reactor vessel can be spherical, square, or rectangular in shape. The reactor is operated, at the top where the hydrogen is combusted with air, at temperatures of about 3000 to 4000 E, which radiates heat into the fluid coke bed and maintains the bed at temperatures of about 1800 to 2800 F. This type of reactor would more generally be operated at average gas phase temperatures of 3000 to 3500 F. and fluid coke bed temperatures of 1900 F. The reactor is suitably lined with refractory material to withstand these temperatures. In this embodiment, hydrocarbon feed is injected into the hot fluidized bed of coke particles and cracked to evolve hydrogen which is utilized as the fluidizing gas and carbon, which deposits on the hot coke particles whereby they gradually grow in size. The evolved hydrogen moves upward in the vessel and is thoroughly mixed with preheated air and combusts to produce a combustion zone which radiates heat directly to the coke bed and to the roof and walls of the reactor. The roof and walls reflect radiated heat into the coke bed. The refractory brick and refractory lining material needed to sustain the heat used in this reactor are of the conventional type used in fabricating high temperature furnaces and in particular the type used in the manufacture of open hearth furnaces used in the manufacture of steel.

In carrying out the high temperature fluid coking process of the present invention, in order to minimize the formation of soot and entrainment and loss of soot from the system, it is important to minimize the bubble size, gas channeling and bypassing of vapors rising through the fluid dense bed and also to minimize the size of the dilute phase of the fluid bed. This is done in the present invention by minimizing the average superficial linear gas velocity of the fluidizing gas through the bed at between 0.1 and 0.7 ft./sec.

The invention is further illust-nated by the following example.

EXAMPLE 1 In order to show the effect of the average superficial linear gas velocity on the production of soot as compared to the production of product coke substantially pure methane gas was injected into a fluidized bed of coke particles at about the same temperature and at different gas velocities and the amount of soot make per pound of carbon feed was measured. Percent conversion of methane to carbon was also measured. The results obtained are given below in Table II.

The above data clearly show that as the average superficial linear gas, velocity of the fluidizing gas in the fluid bed increases, the amount of soot made per pound of carbon feed increases and the conversion of methane to carbon decreases, thus reducing the yield of coke product.

Several additional runs were carried out both with methane feed and other hydrocarbon feeds. The amount of soot make per pound of carbon feed and the conversion of the feed to carbon is reported below in Table III. This table shows that substantially increasing amounts of soot are produced as the average superficial linear gas velocity increases above about 0.7 ft./sec.

The above data clearly show' a substantial increase in soot make as the average superficial linear velocity increases.

Example 2 In an embodiment of the present invention, a suitable reactor containing a fluidized bed of coke particles hav ing an average particle size distribution of 200-350 microns and an average particle size range of microns to 600 microns is used. The fluid bed is about ten feet in depth and about 5 feet in diameter. The bed is fluidized by the evolved hydrogen from the cracking of a hydrocarbon feed. A suitable hydrocarbon feed boiling in the range of about -400 F. is injected through a multiple feed means in the bottom of the bed and contacted with the coke particles which are maintained at a temperature of about 2l002200 F. and is immediately vaporized and cracked to produce coke and about 88% pure hydrogen. The hydrocarbon feed is fed at a rate of 24 barrels per day to maintain an average superficial linear gas velocity of the evolved hydrogen and extraneous gases of 0.3-0.4 ft./sec. The fluid coker is operated at a pressure of 1530 p.s.i.g. The heat to the endothermic cracking reaction is provided by continuously removing part of the coke product and transferring it to a transfer line burner in which an extraneous hydrocarbon fuel is burned, heating the circulated solids to a temperature of 200-400 F. above the temperature maintained in the coking reac tor. The solids are circulated at a ratio of about 30 to 40 to one of the weight of withdrawn coke product. Under these conditions of operation, the soot-make is limited to about 05%. The high quality-high density product coke is recovered. About /5 to /3 wt. fraction of the product coke is ground to a particle size having a particle size range of 75 to 100 microns and is continuously fed back into the fluid coke reactor to maintain the coke particle size in the reactor at the desired range.

Example 3 In a preferred embodiment of the present invention, a relatively shallow, wide diameter fluid coke bed is utilized. In this embodiment a coke bed having a depth of about ft. and a diameter of about 30 ft. is utilized. Particle size distribution of the coke particles in the bed is maintained at about 44 microns to about 1650 microns with the average particle size of the coke particles in the coke bed of about 200-350 microns. Hydrocarbon feed is continuously fed to the coke bed at 24 barrels per hour and cracked to produce carbon which is deposited on the hot coke particles in the fluidized bed and to evolve hydrogen which comprises the fluidizing gas for the bed. This reaction is carried out at substantially atmospheric pressure. The hydrocarbon feed is fed at such a rate as to maintain an average superficial linear gas velocity of the fluidized gas in the bed of about 0.3-0.4 ft./sec. The heat to carry out the endothermic cracking reaction is provided by burning within a suitably lined reactor the by-product hydrogen, which proceeds upward through the bed to the top of the reactor vessel, is mixed with preheated air and burned. The hydrogen and air are burned at an average temperature in the flame area of about 3500 to 4000 F. The hot flame radiates heat to the fluidized bed of coke, to the walls and roof of the reactor. The walls and roof of the reactor reflect radiated heat back into the fluidized bed of coke, maintaining the coke bed at a temperature of about 2l002200 F At this temperature, and the above described average superficial linear gas velocities of 0.3-0.4 ft./sec., the sootmake in the reactor is less than about 0.01 pound of soot per pound of carbon in the hydrocarbon feed. The hydrocarbon feed has a boiling range of about 180 to 400 F. and is injected through multiple hydrocarbon feed inlet means into the hot fluid coke bed and cracked as above described. As the carbon deposits on the hot coke particles in the bed they gradually grow in size and are with drawn. About /5 to /3 of the coke particles are ground to an average particle size of 75-100 microns having a particle size range of 44 microns to 150 microns and are continuously fed back to the coke bed to maintain the average particle size of the coke particles in the bed at about 200-350 microns.

The coke products of the present invention can be used in the formation of electrodes for the aluminum industry. The coke can be used to make Soderberg or prebake electrodes. Suitable electrode formulations can be prepared by grinding a portion of the coke product to form coke fines, mixing the fines with coarse coke aggregate or unground coke as recovered from the reactor and a suitable binder. In the case of prebake electrodes, the formulation would be baked, and in the case of Soderberg electrodes would be fed to the Soderberg process. The process of the present invention produces a high qualityhigh temperature fluid coke with substantially reduced soot production.

The invention is not to be limited by the above description or illustrations presented in the examples, but only by the appended claims.

What is claimed is:

1. A high temperature fluid coking process comprising injecting a hydrocarbon feed into a fluidized bed of coke particles maintained at a temperature of about 1800 to 3000 F., whereby the hydrocarbon feed is cracked to essentially hydrogen and coke, at a rate to maintain an average superficial linear gas velocity of 0.1 to 0.7 ft./sec. to fluidize the coke particles and to substantially reduce the production of soot-like material, said coke depositing on the hot coke particles gradually enlarging them in size to form coke particles having a laminar structure, and recovering high temperature fluid coke.

2. The process of claim 1 wherein the amount of sootlike material produced is kept below 10% based on carbon in feed.

3. A high temperature fluid coking process comprising injecting a hydrocarbon feed into a fluidized bed of coke particles maintained at a temperature of about 1800 to 3000 F., whereby the hydrocarbon feed is cracked to essentially hydrogen and coke, feeding the hydrocarbon at a sutficient rate to maintain an average superficial linear gas velocity of the evolved gases comprising hydrogen through the fluidized coke bed at 0.1 to 0.7 ft./ sec. to substantially reduce the production of soot-like material and to maintain the coke particles as a fluid bed, the residence time of said feed in said bed being suificient to obtain at least conversion to hydrogen and coke, the product coke depositing on the hot coke particles to form coke particles having a laminar structure, and recovering high temperature fluid coke product.

4. A high temperature fluid coking process comprising injecting a hydrocarbon feed into a fluidized bed of coke particles, maintained at a temperature of about 1950- 2300 F whereby the hydrocarbon feed is cracked essentially to hydrogen and coke, feeding said hydrocarbon at a sufficient rate to maintain the average superficial linear gas velocity of the evolved gases at about 0.3-0.4 ft./sec. to substantially reduce the production of soot-like materials and to maintain the coke particles as a fluid bed, the produced coke depositing on the hot coke particles and recovering high temperature fluid coke having a laminar structure.

5. The process of claim 4 wherein the soot-like material produced is less than 5 to 10%.

6. A high temperature fluid coking process comprising injecting a hydrocarbon feed into a fluidized bed of coke particles maintained at a temperature of about 1800 to 2500 F. having a particle size range of about 44 microns to about 1650 microns and an average particle size of about -600 microns, whereby the injected hydrocarbon feed is cracked essentially to hydrogen and coke and said hydrocarbon is fed at a suflicient rate to maintain the average superficial linear gas velocity between about 0.2-0.5 ft./sec., the thus produced coke depositing on said coke particles whereby they gradually grow in size to form spherical coke particles having a laminar structure and recovering high temperature fluid coke.

7. A high temperature fluid coking process comprising injecting a hydrocarbon feed into a fluidized bed of coke particles maintained at a temperature of about 1950- 2300 F., whereby the hydrocarbon feed is cracked to essentially hydrogen and coke, said feed being introduced at a suflicient rate to maintain the average superficial linear gas velocity of the evolved gases at about 0.2-0.5 ft./sec. and at a rate to substantially reduce the production of soot-like material to less than 5% and recovering high temperature fluid coke product composed of spherical particles having a laminar structure.

8. A high temperature fluid coking process comprising injecting a hydrocarbon feed into a fluidized bed of coke particles in a reactor maintained at a temperature of 1950-2300 F. by circulating part of the product coke to a vessel wherein the coke is heated to a temperature 200 to 400 F. above the temperature in said reactor and returning the thus heated coke to the coking reactor to provide the endothermic heat added to carry out the coking reaction as sensible heat of the circulated coke, whereby the injected hydrocarbon feed is cracked essentially to hydrogen and coke, said feed being introduced at a suflicient rate to maintain the average superficial linear gas velocity of the evolved gases at about 0.2-0.5 ft./sec. and at a rate to control the production of sootlike material to less than about 5%, the thus produced coke depositing in layers on the coke particles gradually increasing them in size, recovering the high temperature fluid coke, grinding part of the coke to make seed coke and recycling the seed coke to the reactor.

9. The process of claim 8 wherein /5 to /3 of the product coke is ground to make seed coke and is recycled to maintain the average particle size in the coke bed of 150-600 microns.

10. A high temperature fluid coking process comprising injecting a hydrocarbon feed into a fluidized bed of coke particles at a temperature of about 19502300 F., said particles being maintained at this temperature by combusting the product hydrogen in a section of the reactor free of solids by mixing with air and radiating heat to the fluid coke bed from the combustion zone and the Walls and roof of the reactor whereby the hydrocarbon feed is cracked on contact with the hot coke particles essentially to hydrogen and coke, said feed being fed 10 at a suflicient rate to maintain an average superficial linear gas velocity of 0.20.5 ft./ sec. in the bed, the production of soot-1ike material maintained at less than 10%, the thus produced coke depositing in layers on the hot coke particles and said particles increasing in size and recovering high temperature fluid coke product.

References Cited by the Examiner UNITED STATES PATENTS 2,690,963 10/1954 Herbst 23-212 2,709,676 5/1955 Krebs 208-127 2,893,946 7/1959 Brown 208127 DELBERT E. GANTZ, Primary Examiner.

A. RIMENS, Assistant Examiner. 

8. A HIGH TEMPERATURE FLUID COKING PROCESS COMPRISING INJECTING A HYDROCARBON FEED INTO A FLUIDIZED BED OF COKE PARTICLES IN A REACTOR MAINTAINED AT A TEMPERATURE OF 1950-2300*F. BY CIRCULATING PART OF THE PRODUCT COKE TO A VESSEL WHEREIN THE COKE IS HEATED TO A TEMPERATURE 200 TO 400*F. ABOVE THE TEMPERATURE IN SAID REACTOR AND RETURNING THE THUS HEATED COKE TO THE COLING REACTOR TO PROVIDE THE ENDOTHERMIC HEAT ADDED TO CARRY OUT THE COKING REACTION AS SENSIBLE HEAT OF THE CIRCULATED COKE, WHEREBY THE INJECTED HYDROCARBIN FEED IN CRACKED ESSENTIALLY TO HYDROGEN AND COKE, SAID FEED BEING INTRODUCED AT A SUFFICIENT RATE TO MAINTAIN THE AVERAGE SUPERFICIAL LINEAR GAS VELOCITY OF THE EVOLVED GASES AT ABOUT 0.2-0.5 FT./SEC. AND AT A RATE TO CONTROL THE PRODUCTION OF SOOTLIKE MATERIAL TO LESS THAN ABOUT 5%, THE THUS PRODUCED COKE DEPOSITING IN LAYERS ON THE COKE PARTICLES GRADUALLY INCREASING THEM IN SIZE, RECOVERING THE HIGH TEMPERATURE FLUID COKE, GRINDING PART OF THE COKE TO MAKE SEED COKE AND RECYCLING THE SEED COKE TO THE REACTOR. 